Conventionally, such a printing apparatus has been known widely that forms an image on a printing medium using a thermal head. This type of printing apparatus uses an indirect printing scheme for forming an image (mirror image) on a transfer film using an ink ribbon, and next transferring the image formed on the transfer film to a printing medium, or a direct printing scheme for forming an image directly on a printing medium using an ink ribbon.
Generally, in such a printing apparatus are inserted an ink ribbon cassette storing an ink ribbon (film-shaped medium) laid between a supply spool and a wind-up spool, and similarly, a transfer film cassette storing a transfer film (film-shaped medium) laid between a supply spool and a wind-up spool.
In this type of printing apparatus, such a technique is disclosed that a certain tension is added to the ink ribbon corresponding to a variation in the diameter (roll diameter) of the ink ribbon wound around the spool (for example, see Patent Document 1).